Please plan to overnight in AMS on the outbound, ideally by not taking the last KLM flight from GLA to AMS of the night. There are reasonable/pleasant hotels at AMS or you can go into town for the evening. In fact, if you have an afternoon departure, you could even go to The Hague for the night since it's a short and easy train ride with frequent service.

Coming a bit late to this thread: I was in a similar situation to the OP last year. Was on the last easyjet flight of the day to INV to start a trip from there. By about 11pm it Was cancelled. At that time there was no longer any sensible way of getting to INV (two G&Ts in the lounge didn't help and public transport to the far end of Britain is surprisingly bad).

In the end we made our way directly to LHR the next morning, arriving 3.5 hours early. After providing evidence of the cancelled easyjet flight and about 30 minutes of wild typing and calling in supervisors, everything turned out well. At the time it appeared like standard procedure to help passengers in a situation like this, however us being on a non-BA flight initially was what required the supervisor approval.

It was a pretty stressful experience - would not be keen to repeat that one...

exEU is all about risk, I think ex DUB is probably one of the lower risk options. There must be over 50 flights a day between EI, BA and FR, from any ‘London’ airport you care to consider. If an 18/1900 flight went wrong, there is still a good chance of getting to DUB that evening, I would say. Bar a weather disaster, in which case all bets would be off and the chance of a re-route pretty good anyway.

no that’s not how it works. It is still two separate tickets which happens to be all under the TA’s one booking code/wrapper. The KL flight may show under BA MMB ( I have similar TA bookings which mix BA and LS and the LS flight shows in ba mmb) but it is purely there for information. If it was truely one ticket then the price would be radically different from the low exAMS price that the OP would like to take advantage of.

I agree and that’s why I was surprised by the comments upthread that BA would likely have been helpful if the OP had turned up at LHR. But was also happy and learn from those who have been in such situations. Wonder if the helpfulness would also extend to a non BAEC member.

the situations where ba has allowed starting at LHR tend to be where there is large amount of disruption and the positioning flight or first leg is cancelled or heavily delayed. It shows the advantage of positioning on BA rather than another airline as you are already at LHR so can attempt to deal with the situation and are probably more likely to be shown so leniency since it is all on the same airline. If positioning on another airline and that other airline flight was cancelled I would not expect any help from BA to allow me to start at LHR.

the point I was commenting on above is different tho and relates to protection across flights where they appear together in the booking due to being booked by a TA.

The OP’s positioning was on KLM yet corporate-wage-slave, whose knowledge I would not doubt, was of the opinion BA would have likely accepted an LHR departure for just the change fee - that bit surprised me to be honest.

Yes 95 and 105. Am kinda surprised too and also glad the OP did not have to test this!